It is known that automation units can comprise at least one electric motor connected to a mechanical member either by means of a reduction device, or directly. It is known that eliminating an intermediate reduction stage is a positive factor in that it allows to limit play, increase precision, reduce the power consumed as well as to use simpler systems and/or with fewer components.
Generally, systems that have a very modest reduction between the motor member and the mechanical member, in the order of no more than around ten units, are also included in direct motion systems. More precisely, at least in the present invention, those systems in which the inertia of the motor is higher than twice the inertia of the mechanical member are considered direct motion systems.
In direct motions, the electric motors, which are generally and advantageously, but not only, the brushless type, can be subject to inertial imbalances due to the presence of variable loads inside the round angle of the mechanical member, or part of said round angle. The variable loads are generated by the geometries of the individual device to be commanded.
The movements of these systems can have a fixed duration cycle, or a variable duration cycle.
It must also be taken into consideration that the cycles can be carried out with a high cadence in the unit of time, for example inside a minute.
Normally the movements of these systems must be very precise, both to prevent possible interference between the different mechanical members of the automation units, and also for the correct execution of the different steps of the method that the individual cycle achieves. It should be noted that a cycle can concern one round angle or more, or it can be a fraction of a round angle, given that it is the sum of said fractions making up one round angle, or more, of the mechanical member.
According to the present invention, by mechanical members we mean drums, cranks, pantographic systems, cams or other, according to the specific requirements of the processes that have to be done.
Document EP-A2-1,815,972, which can be considered the state of the art for the present invention, describes a control system for a pressing line in which the speed of the motor can be varied on the basis of a pressing or non-pressing condition of the line, on which the preamble of the independent claims is substantially based.
However, in general, one disadvantage of the state of the art is the fact that the control of the inertia of the individual automation unit is carried out considering the inertia constant for the whole cycle.
A second disadvantage is that the cycle is not analyzed in sub-phases, for example referring to the round angle of the mechanical member, but considering it as a single phase. Other disadvantages derive from different performances depending on the thermal drift, the wear and tear, the mechanical deformations, the variability of the friction, the variability of the resistances met and cogging of the motor.
The command and control systems of the known type, considering the operating cycle as a single phase, do not therefore allow to carry out in a detailed and point-by-point way the pre-defined program corresponding to the sub-phases that, all together, make up the cycle.
One purpose of the present invention is to supply a command and control method that guarantees that the different movements of the mechanical member, in relation to each sub-phase of a cycle, are as precise as possible in terms of angular position, angular speed and acceleration of the mechanical member.
Another purpose of the present invention is to achieve a command and control method that takes constant account of the different drift effects, and can intervene each time in a pre-defined and memorized program, or in some characteristic factors thereof, said intervention having the purpose of maintaining precision, for each sub-phase, in the operating values (speed, acceleration, position etc.) of the mechanical member.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.